Building construction sites for large buildings frequently employ aerial lift equipment for lifting operatives to elevated locations for, for example, the installation of overhead pipe work during the construction of a building.
A typical aerial lift may comprise a mobile elevated work platform (MEWP) having an extendable boom which has an elevator basket or cage for housing operatives secured to the end of the boom. The basket or cage may contain a control panel which permits a user standing in the basket or cage to manoeuvre the basket or cage to a raised location which facilitates the carrying out of work. The boom is typically raised by a powered hydraulic system on the vehicle.
The controls in elevator baskets typically include an emergency stop and a foot operated safety switch which needs to be closed before the controls may be operated. If the foot safety switch is released the movement of the basket ceases immediately and the MEWP engine continues to run. If the emergency stop safety switch is triggered both the basket and MEWP engine are stopped. In some situations, operators can become trapped between the MEWP basket and an overhead structure before they can either remove their foot from the foot safety switch or operate the emergency stop. Operators trapped in this way can be crushed sometimes fatally.
In EP-A-2096 078, the present applicant has described a safety device comprising a tensioned wire or cord arranged proximate to the controls and an auxiliary safety switch connected in series with the foot safety switch. The operation of the auxiliary safety switch via the tensioned wire or cord stops the movement of the basket and may also operate an alarm to indicate to other parties the fact that the safety device has been operated.
The present invention provides a safety device for an overhead work platform and which has an improved alarm control system.